Radio receiver



Sept. 28, 1937. I, DRAKE 2,094,233

RADIO RECEIVER Filed April 23, 1954 3 Sheets-Sheet 1 EnedJ/aqe T 67 BandpassJfoqe 5 I l l I u I ,2 l S I F. H. DRAKE RADIO RECEIVER Sept. 28, 193 7.

Filed April 23, 1954 3 Sheets-Sheet: 2

Sept. 28, 193 7 DRAKE 2,094,233

RADIO RECEIVER Fiied April 23, 1934 3 Sheets-Sheet 5 invention will be apparent from Patented Sept. 28, 1937 UNITED STATES PATENT OFFICE RADIO RECEIVER Frederick H. Drake,

Boonton Township, Morris Application April 23,

15 Claims.

This invention relates to radio receivers and particularly to a multirange radio receiver of the type employing a plurality of cascaded radio amplifier stages, some or all of the stages being tunable over the frequency bands.

Universal radio receivers, that is, radio r ceivers adapted for operation over a number of frequency bands by plugging in gang coil sets, are widely used today in both civil and military airplanes but it usually is impossible for the pilot or radio operator to change coil sets when the receiver is remotely controlled. Operation on at least two frequency bands is necessary for the reception of beacon signals and for communication with ground or other planes.

An object of the present invention is to provide a multirange radio receiver including a bandchanging system of improved electrical and physical design. Another object is to provide a double range coupling system for use in such a receiver, the coil system including circuit elements for operation on either of two frequency bands and a switching system which may be locally or remotely controlled, as desired, to select the operating range. A further object is to provide a dual coil set adapted to be used with a universal or multirange receiver, the dual coil set including an assembly of a number of shielding closures which each house two separately shielded coil units with a switch unit in the section of the closure that contains the low frequency coil set, and a control shaft for all of the switch units, the shaft being of insulating material and threaded through all of the switch units after the shielding closures are alined in a close assembly. More particularly, an object is to provide a dual coil unit for interchangeable use with the single coil units of known universal receivers, the double coil unit including two sets of coils and a switching system which may be adjusted by local or remote control for selecting the frequency range, and the double coil unit being of approximately the same size as the prior single coil units.

These and other objects and advantages of the the following specification when taken with the accompanying drawings in which:

Fig. l is a fragmentary circuit diagram of a dual range radio frequency amplifier;

Figs. 2 and 3 are schematic views corresponding to Fig. 1 but illustrating only those circuit elezrents which are operative when the amplifier is adjusted for reception in, respectively, the low frequency and the high frequency band;

Fig. 4 is an end elevation of a remotely con- 1934, Serial No. 722,002 (01. 179171) trolled radio receiver including a remotely controlled dual range coil set embodying the invention;

Fig. 5 is a perspective view of the coil set of Fig. 4, but showing a local control handle substituted for the remote control;

Fig. 6 is a top view, with parts in section, of the coil set assembly, the switch rod being shown in partly removed position;

Fig. 7 is a sectional view on line 1-7 of Fig. 8 of a tuned stage coupling unit, the low frequency shield can being removed;

Fig. 8 is an end view of a tuned stage coupling unit as seen after removal of the low frequency shield can;

Figs. 9 and 10 are somewhat schematic views of the circuit elements of the tuned and bandpass couplings, respectively;

Fig. 11 is a perspective view of a coil form for the high frequency transformer;

Fig. 12 is a fragmentary detail View of the switch shaft and operating member.

The particular embodiment of the invention which will be described is a military aircraft radio receiver employing plug-in coils such as described in the U. S. Patent No. 1,968,557, dated July 31, 1934, of John E. Johanson, but it will be apparent that the invention may be incorporated in receivers designed for operation over only the two frequency bands of the dual coil assembly. The frequency bands used in military equipment are 224 to 400 kilocycles for cross-country navigation and 4200 to 7700 kilocycles for communication within the group of military planes. The prior practice is indicated by the Johanson patent which describes an assembly of single range coils that may be plugged into a receiver to provide all of the interstage couplings for adapting the multistage amplifier for operation over one band. In accordance with this invention, a single assembly of coils and switches permits operation within either of the two bands, and the switches may be adjusted by either a local or remote control in accordance with the relative location of the receiver and the operators seat.

The electrical design of the dual range amplifier is shown diagrammatically in Fig. 1, in which the legends Tuned stage and Band-pass stage indicate the shielded coil assemblies which constitute the coupling systems of the tuned and band-pass stages of the amplifier. The several tubes and circuit elements exterior to the shielded assemblies are shown in lighter lines to differentiate the permanent elements of the universal receiver from the removable elements of the coil assembly.

The several tuned stage coil units are of identical design and include shield cans S, S which house the transformers and switch, the assembly having terminals l, 2, 3, and t for establishing connections to the permanent wiring of the receiver when the dual coil set is plugged into the receiver. The band-pass coupling system includes shield cans S1, S1 which house the coupling impedances and a switch, the unit having terminals 5, 6, 1, and 8 for association with the permanent wiring of the receiver.

The low frequency transformer 9 and a pair of single pole, double throw switches, s, s are housed in the upper shield can S, and the high frequency transformer H3 is housed in the lower shield can S of the tuned coupling system. The high potential terminals of the primaries of transformers 9, If] are connected to the respective contacts L0 and HI of switch s and the contact arm s is connected to terminal I, while the low potential terminals of both primaries are connected to terminal 2. The low potential terminals of both secondaries are grounded on the shield cans and terminal 4, while the high potential terminals are connected to contacts L0 and 1-11 of switch s which has a contact arm connected to terminal 3.

In the band-pass coupling unit, the high frequency choke H and low frequency choke l2 are serially connected between the terminals 5 and 6, and a coupling capacity 53 is connected between terminals 5 and i. The switch unit of the band-pass coupling is preferably identical with the switch unit of the tuned couplings, but the pair of switches are, in effect, single pole, single throw switches as the contact LO of switch s is open, as is the contact HI of switch s. A condenser IQ is connected between terminal 8 and contact LO of switch 8 and a grid leak i5 is connected between terminals l and 8. A resistance I6 is shunted across the high frequency choke i l to broaden the resonance point of the stage when the switches are adjusted for reception in that range.

The terminal 3 of each tuned coupling unit is connected to the control grid of the associated tube T through a coupling condenser I! and the terminal 1 of the band-pass stage is connected directly to its associated control grid. The

ganged tuning condensers C of the tuned stages are shunted between the terminals 3 and ground, and the antenna A is connected to the terminal 3 of the first tuned unit through an adjustable condenser CA. The terminal 6 of the band-pass unit and terminals 2 of all except the first unit are connected to the plate current supply, indicated as +B. A condenser C is connected between terminals l, 2 of the first tuned unit and cooperates with the primaries of transformers 9, it to constitute a dummy tube.

This feature is of particular importance since, for approximately the same gain on both ranges, the transformation ratio of the transformers 9 is several times the transformation ratio of transformers l9. In the particular receiver model designed for military use, the ratio for low frequency transformers for the 224 to 400 kilocycle band was 4 to 1, while the ratio for the higher frequency band of 4200 to 7700 kilocycles was 1 to 1. This difference in transformation ratios results in a substantial difference in that capacity which is reflected into the tuned circuits from the plate-cathode capacity of the preceding tube. Except for the dummy tube eifect provided by the capacity C in the input stage, it would be necessary to adjust the value of the antenna condenser CA when changing from one band to the other. By adjusting capacity C to the value of the plate-cathode capacity of tubes T, an adjustment of condenser CA which alines the input stage with the other tuned stages on one band will hold good for the other band.

The circuit connections established by the alternative adjustments of the switch system will be apparent from Figs. 2 and 3 which omit those elements of the coupling systems which are inoperative when the receiver is adjusted for reception on, respectively, the low frequency and the high frequency bands. The switching in the tuned stages substitutes one transformer for the other, in known manner, but the switching of the band-pass stage presents several features of novelty. The chokes are designed to resonate at or near the lower limit of the respective frequency bands to increase the amplification in that region, thus compensating for the decrease in amplification of the tuned stages at the lower limit of each band. As shown in Fig. 2, the adjustment for the lower frequency band places the high frequency choke ii in series with the low frequency choke l2. The inclusion of the high frequency choke I l in the plate circuit when operating on the lower frequency range does not materially affect the operation as the high fre quency choke will present but a low impedance at the lower frequencies and, in general, the impedance of the lower frequency choke l2 may be reduced somewhat below the value which would be appropriate if the high frequency choke H were shorted. The gain of the amplifier stage at low frequencies is usually excessively high and the condenser M is therefore shunted across the grid leak I5 by switch 8 to cooperate with the coupling condenser l3 to form a voltage divider. That fraction of the available voltage developed across the chokes ll, i2 which is app-lied to the grid of the succeeding tube T may be adjusted to any desired value by an appropriate choice of the values of condensers i3 and M. For operation on the higher frequency band, the switch s shorts out the low frequency choke B? (see Fig. l) and switch 8 opens the circuit of the voltage divider condenser i l, thus placing the maximum voltage upon the succeeding tube.

As shown in Fig. 4, the invention is particularly adapted for use with the small, high gain receivers employed on military aircraft. As described in detail in the J ohanson patent, such receivers comprise a metallic housing or case 26 which is carried on a shock-proof mounting 2!, the case having a portion of one side wall cut away to permit the introduction of the coil unit U which determines the operating range of the receiver. The receiver may be adjusted over the selected band by a remote tuning control TC and, when the coil assembly U is of the dual range type contemplated by this invention, the frequency band may be adjusted by the remote band control BC.

The coil assembly U includes a plurality of dual coil units, in shield cases S, S and S1 S1, which are mounted on a metal box 22 provided with a flanged edge having openings 23 (see Fig. 5) for receiving pins on the case iii and latches 24 for locking engagement with the pins. The particular assembly shown in Figs. 5 and 6 is designed for an amplifier including a tuned input circuit, a band-pass circuit and three tuned circuits. The electrical design of these circuits is that which is shown diagrammatically in Fig. 1, and the physical construction of the high frequency band coil units and shield cans S, S1 is substantially identical with that previously employed for a single range coil assembly such as described by J chanson. The transformers H] are solenoidal windings on tubular forms 25 (see Fig. 6) having flanged ends secured to the closures 26 of the shield cans S. The terminals 2, 3, 4 of each unit take the form of sleeves or sockets in the flanged end of the tubes 25 (see Fig. 7), the sockets fitting over pin terminals of the permanent wiring of the receiver when the assembly is plugged in.

Integral lugs 21 are formed on the cans S and these lugs are threaded to receive the screws for attaching the shield cans S. The low frequency transformer 9 takes the form of two small flat or universal wound coils on an insulating rod 28 (see Fig. 6) which is secured to the end of the shield can S. Attention is directed to the fact that the axis of the transformer 9 is normal to the junction plane of the cans S, S. This is important in a high gain receiver, as it reduces the tendency towards interstage couplings. The universal wound type of low frequency transformers is also of great importance as it permits the mounting of the low frequency range coils and switches in a space not appreciably greater than that occupied by the handle used when a series of single range coils are mounted on a fiat plate. The cans S and S1 extend into the boxlike plate 22, and these cans are secured to the plate by screws 29 (see Figs. 5 and 6), insulating washers 30 being provided to prevent any coupling between adjacent coil assemblies.

The switch elements present a difficult design problem for several reasons. Small size is essential but an exceedingly low electrical resistance is necessary to preserve the high selectivity characteristics of the low resistance coils. All switches must be ganged for simultaneous operation, but the switches and the common operating members must be of such construction that there will be no coupling between adjacent coil units.

As best shown in Figs. '7 and 8, each switch is mounted on the end of its associated coil can S and includes a pair of spaced plates 3| of insulating material which have circular openings providing bearings for an oscillating switch cylinder 32 of insulating material in which the pins or switch contacts 33 are embedded. The portion of cylinder 32 which lies between the plates 3| is of somewhat enlarged diameter and carries stop lugs 34 for engagement with a pair of the rivets 35 which secure the plates 3| to each other.

Two sets of pairs of angular contact straps 36, 31 and 36, 31 are symmetrically arranged on the insulating plates 3|, the ends of the straps which overlie the cylinder 32 being bent at right angles to the main portion of the straps to form contacts for engaging the pins 33. The straps are formed of resilient material, such as phosphor bronze, to obtain a good contact engagement of the switch elements. The pairs of contact straps 3E, 31 at the side of the switch adjacent the transformer 9 correspond to the pair of contacts HI, LO shown in the circuit diagram, Fig. 1, and the contact straps 36', 31 of each pair at the opposite face of the switch are joined by jumpers 38 and, in cooperation with the contact pins 33, correspond to the switch arms s, s of Fig. 1 which are connected to terminals and 3 of the coil assemblies.

The switch cylinders 32 are provided with noncircular and preferably square apertures 39 for receiving an operating shaft 40 of similar cross section. The shield cans S have openings in axial alinement with the switch cylinders and, as indicated graphically in Fig. 6, the shield coil assemblies are first mounted on the plate 22 and the shaft 40 is then threaded through the series of switch cylinders. It is essential that the shaft be of insulating material, such as a molded synthetic resin, to prevent interstage couplings. A flanged metal sleeve 4| of circular cross-section is secured to the outer end of the shaft 40 and has a counterbore 42 (see Fig. 12) of square crosssection for receiving the correspondingly shaped end of an operating member 43. The shaft 40 has a floating bearing in the several switch cylinders and is restrained from longitudinal movement by a cap plate 44 which is secured to the plate 22, the plate 44 having a threaded sleeve 45 for receiving the threaded cap 46 which secures the operating member 43 to the shaft. As shown in Fig. 5, a short handle 41 is secured to the member 43 for a local control of the switches but, as shown in Figs. 4 and 12, the operating member may be fixed to the end of the flexible shaft of a remote control unit.

The electrical connections between elements in the two coil cans of each unit are conveniently made by cap terminals 48 which are secured to the upper end of the coil form 25 and project through openings 49 in the end of can S. In assembling a unit, the transformer 9 and switch are mounted on can S and the wiring to the appropriate cap terminals 48 of coil form 25 is completed after the coil form is mounted in the can S by closure 26.

In the band-pass coupling system, all of the coupling impedances may be mounted in the same can S1, and only the switch elements are housed in the smaller can S1.

While the drawings illustrate a preferred cons ruction for a dual coil set which is to be used with a universal radio receiver for aircraft, there is some latitude in the electrical and physical design when the limitations as to size and weight are less rigid. The invention is not limited to the tuned radio frequency type of amplifier illustrated in the drawings as it will be apparent that the same methods and structural arrangements for switching from one band to another are useful in superheterodyne receivers.

I claim:

1. A multistage radio amplifier including a plurality of tubes, a tunable input system and a substantially identical tunable interstage coupling system, each tunable system including a pair of radio transformers of different transformation ratios and switch means for connecting a section of a gang tuning condenser across the secondary of one or the other of said transformers and for simultaneously connecting the primary winding of the corresponding transformer of the interstage coupling system in the plate circuit of the tube which works into the said system, characterized by the fact that the antenna is connected to the control grid of the input tube through an antenna trimming condenser, and means whereby a condenser simulating the platecathode capacity of the tube working into said interstage coupling system is switched across the primary winding of that transformer of the tunable input system whose secondary winding is connected across the tuning condenser section of the input stage.

2. In a radio amplifier, the combination with a plurality of tubes, a section of a gang tuning condenser connected across the input electrodes of each of said tubes, and an interstage coupling system between two of said tubes comprising a pair of transformers of different transformation ratios and means for rendering either transformer operative and the other inoperative as a coupling element, said means including switch means and circuit elements for connecting the primary of either transformer in the plate circuit of the first tube and the secondary of the same transformer across the input electrodes of the second tube of the pair of tubes coupled by said interstage coupling system, of an antenna connected to the control grid of the tube of the input stage of said amplifier, a tunable system for said input stage including a pair of transformers and switch means substantially identical with the corresponding elements of said interstage coupling system, means adjustable in accordance with the antenna capacity to aline the tuning of the said two systems when one set of corresponding transformers is operative, and means compensating for the difference in the transformation ratios of said pairs of transformers to maintain the tuning alinement of said systems when the same are adjusted for reception over the other band.

3. A radio amplifier as claimed in claim 2, wherein said compensating means comprises a condenser adapted to be connected by the switch means of said tunable system across the primary of that transformer which is rendered operative by the said switch means.

4. In a radio amplifier, the combination with a plurality of tubes, and a condenser tuned impedance network working into one of said tubes and including switch means operative to alternative positions to select a higher or lower frequency band over which said network may be tuned, of a band pass coupling system working out of one of said tubes, said band-pass coupling system including a plurality of radio frequency chokes, second switch means ganged with the first switch means and circuit connections for alternatively connecting in the plate circuit of a tube working into said coupling system certain of said radio frequency chokes having a high impedance for the respective tuning bands of the said tuned network, a condenser coupling the plate of the last mentioned tube to the succeeding tube of said amplifier, a second condenser, and contacts controlled by said second switch means for shunting said second condenser across the input electrodes of said succeeding tube when the said ganged switch means are adjusted to condition said amplifier for the reception of signals in the lower frequency band.

5. A radio amplifier as claimed in claim 4, wherein said radio frequency chokes comprise a low frequency band choke and a high frequency band choke in series in the said plate circuit for reception on the lower frequency band, and said second switch means short circuits said low frequency choke when adjusted for operation on the higher frequency band.

6. In a radio receiver, a double range tuned amplifier stage comprising a tube having a tuning condenser shunted across the input electrodes thereof, a pair of transformers having secondaries adapted to be tuned over respectively a high and a low frequency band by said condenser, switch means for alternatively connecting one or the other of said secondaries across said tuning condenser, shielding means enclosing the high frequency band transformer, and a single shielding can housing the switching means and the low frequency band transformer.

'7. A'radio receiver as claimed in claim 6, wherein said shielding means comprises a can having an apertured end, said low frequency band transformer comprises a pair of universal wound coils having their common axis normal to said closed end, and the coil can housing said low frequency band transformer and switch means is an open-ended can having its open end resting on and secured to the said end of the can enclosing said high frequency band transformer, the electrical connections between said latter transformer and the switching means extending through the said apertures.

8. A radio receiver as claimed in claim 6, wherein said switching means comprises an oscillating switch cylinder mounted in said single shielding can-and having a non-circular axial bore, and a switch shaft of non-circular cross section extending through said bore, said can having openings in axial alinement with said switch cylinder to permit the insertion and removal of said switch shaft after said can is placed over said low frequency band transformer.

9. A dual range multiple coil assembly comprising a plurality of sets of low frequency and high frequency band impedances, a shield can housing each of said impedances, each low frequency impedance and its shield can being mounted on the shield can of the associated high frequency band impedance, a mounting plate of boxlike form having a flanged edge for attachment to a radio receiver, said low frequency band shield cans being positioned within and secured to said plate, switch means in each of said low frequency shield cans for selectively determining the set of impedances to be operatively connected to the receiver, and a common operating shaft for all of said switch means insertable through said plate and low frequency cans after the latter are secured to said plate.

10. A dual range multiple coil assembly as claimed inclaim 9, wherein said switch shaft is formed of insulating material, thereby to suppress coupling between impedances housed in different coil cans.

11. A dual range multiple coil assembly adapted to provide the interstage couplings for a plurality of cascaded radio frequency amplifier tubes, one

unit of said assembly comprising a pair of transformers adapted to be tuned over different frequency hands by the same tuning condenser, a second unit comprising a pair of chokes having high impedances for the respective tuning bands v of said transformer, a switch means for each unit adjustable to determine the frequency band transmitted thereby, means for simultaneously adjusting both of said switch means, and means adjustable by the switch means associated with said chokes to reduce the efficiency of signal transmission When the said switch means are adjusted for reception of signals within the lower frequency band.

12. In a dual range coil assembly adapted to provide the interstage couplings for a plurality of cascaded radio amplifier tubes, a plurality of units each comprising a high and a low frequency transformer, the former being solenoidal wound coils and the latter being universal wound coils, a shield can for each of said transformers, a set of terminals adapted to complete the electrical connections of each unit to an amplifier,

and gang switch means, contained in one of the shield cans, adjustable to connect either the high or the low frequency transformer of each unit to its associated set of terminals, the switch means of each unit being mounted in the shield can housing the low frequency transformer.

13. A coil assembly comprising a plate, a series of coil cans alined on and secured to said plate, a low frequency transformer and a switch in each of said cans, a second set of coil cans secured to the respective cans of said series, a high frequency transformer in each can of said second set, terminals carried by each can of the second set, circuit elements connecting said switch and transformers to the associated set of terminals, each switch being operable to connect either of its associated transformers to the set of terminals, and a common operating shaft for all of said switches.

14. A coil assembly as claimed in claim 13, wherein said series of coil cans have openings in alinement with the switches mounted therein, and said operating shaft extends through the said openings and the said switches.

15. A coil assembly as claimed in claim 13, wherein said shaft is of insulating material and extends into all cans of said series in proximity to the low frequency transformers housed therein.

FREDERICK H. DRAKE. 

